New ternary ThCr2Si2-type iron–selenide superconducting materials: Synthesis, properties and simulations

Very recently, the first ThCr2Si2-type ternary superconductor K0.8Fe2Se2 with enhanced TC ∼ 31 K has been discovered. This finding has stimulated much activity in search for related materials and triggered intense studies of their properties. Indeed, very soon superconductivity (TC ∼ 28–32 K) was also found in the series of related ternary systems (so-called 122 phases) such as CsxFe2−ySe2, RbxFe2−ySe2, (TlK)xFeySe2, and (TlRb)xFeySe2, which formed a new group of superconducting iron-based materials without toxic As. In this paper the recent progress in synthesis of 122-like iron–selenide systems and in experimental research of their properties is reviewed. Available theoretical data on electronic, magnetic, and elastic properties of this newest group of superconducting materials are also discussed.

► Very recently the newest 122-like group of FeSe-superconductors was discovered.
► The progress in synthesis and research of these phases is reviewed.
► Theoretical data on properties of these newest superconductors are discussed.